This invention relates to a Cathode-Ray Tube (CRT) fluorescent material and its method of manufacture wherein the surface properties of the fluorescent material are modified, while maintaining fluorescent functionality, to allow uniform fluorescent material film formation during CRT face-plate coating.
Various coating methods have been developed for forming a fluorescent material coating on the face-plate of a color CRT. Among them, the slurry method is the most often used. In the slurry method, a face-plate is coated with a fluorescent film as follows. Ammonium dichromate (ADC) or like substance is added to an aqueous solution of fluorescent material particles and polyvinyl alcohol (PVA) to make a fluorescent material suspension (slurry). The inner surface of the face-plate is coated with this fluorescent material suspension. The coated surface is then exposed to ultra-violet light through a shadow-mask causing the exposed areas to oxidize and harden. Since the unexposed fluorescent material particles do not react, they are sprayed off with water to develop the surface. In this fashion a prescribed fluorescent pattern is formed on the face-plate.
In the slurry method, the entire panel including the face-plate was traditionally heated to about 38.degree. C. to 40.degree. C. Recently, in order to increase production by reducing drying time after exposure and development, it has become common to dry the panel including the face-plate by heating it to the high temperature of 55.degree. C. to 60.degree. C. during the drying step.
However, by drying the fluorescent coating at these high temperatures, local thining of the fluorescent material and open spots occur more frequently in the coating resulting in a reduction in production yield. Therefore, fluorescent material particles with modified surfaces, that allow a uniform fluorescent coating to be formed without open spots even when the panel is dried at the high temperature of 55.degree. C. to 60.degree. C. and maintain fluorescent functionality, have long been sought.
The present inventors discovered that the above mentioned problems could be solved by attaching large quantities of electrolytes, which are sulfates, nitrates, or chlorides of alkali metals or alkaline-earth metals, to the fluorescent particles, rather than by methods of forming a fluorescent coating such as adding small amounts of aqueous zinc sulfate solution to the fluorescent material slurry in the slurry method disclosed, for example, by Japanese Non-examined Patent Publication No. 52-67569 issued Jun. 4, 1977. The present invention was completed as a result of this earnest research.
Consequently, the object of this invention is to provide a CRT fluorescent material and its method of manufacture wherein fluorescent particle surfaces are modified, while maintaining fluorescent functionality, to allow formation of a uniform CRT face-plate fluorescent coating, even when it is dried at panel temperatures of 55.degree. C. to 60.degree. C.